Hydraulic time relay for hydraulic systems

ABSTRACT

A hydraulic time relay for hydraulic systems with a throttle plug installed so that it can move to and fro along its axis.

United States Patent Landenzon et al.

HYDRAULIC TIME RELAY FOR HYDRAULIC SYSTEMS Inventors: Boris Yakovlevich Landenzon, Moskovsky prospekt, 238, kv. 1; Rafail Alexandrovich Filatov, ulitsa Girshmana, 18, kv. 8, both of Kharkov, U.S.S.R.

Filed: Mar. 9, 1971 Appl. No.: 122,547

Related U.S. Application Data doned.

U.S. Cl ..9l/38, 91/11 Int. Cl ..F01b 29/04, F15b 21/02 Field ofSearch ..9l/38, ll

References Cited UNITED STATES PATENTS 2,605,751 8/1952 Perry et al. ..92/11 Amen Continuation of Ser. No. 822,616, May 7, 1969, aban- 1151 3,656,404 [451 Apr. 18, 1972 Hydraulic Handbook Trade and Technical Press Ltd. 1960 pp. 374- 379.

Primary Examiner-Mark M. Newman Assistant Examiner- Ronald B. Cox

[5 7] ABSTRACT A hydraulic time relay for hydraulic systems with a throttle plug installed so that it can move to and fro along its axis.

2 Claims, 14 Drawing Figures PATENTEDAPR 18 I972 656,404

SHEET 02 3F 10 PATENTEDAPR 18 e SHEET mar 10 WNH/ PATENTEBAPR 18 1912 SHEET USUF 1O PATENTED R 18 I912 3,656,404

' SHEET UBUF 10 PATENTEDAPR 18 m2 SHEET OSUF 10 w mt QQ w N5 P TEN EDAPR 18 1972 SHEET llJUF 10 #Gt B 80 QQ E v E HYDRAULIC TIME RELAY FOR HYDRAULIC SYSTEMS This application is a continuation of Ser. No. 822,616, filed May 7, 1969, now abandoned.

The present invention relates to hydraulic devices, and more specifically to hydraulic time relays intended for use in the hydraulic systems of machines in which fluid flow directed to any element of the system is to be passed with an adjustable time delay and not all at once.

There exist hydraulic time relays in which a plunger, which also acts as a spool valve, checks the flow of working fluid and passes it only after a definite volume of fluid has been displaced from the relay barrel through the orifice of the throttle plug into the line of the hydraulic system. The relay barrel is filled with working fluid through a fluid-inlet check valve from the same line of the hydraulic system. The time delay is adjusted by varying the setting of the throttle plug.

Such hydraulic time relays (especially those using mineral oil as the working fluid) suffer from a number of serious disadvantages.

A major disadvantage is that over extended time delays (which correspond to minimum flow rates of the working fluid passing through the throttle plug of the relay) the cross-sectional area of orifice in the throttle plug is severly constricted, so that after a few cycles of relay operation the orifice in the throttle plug becomes clogged or fouled by suspended solids, with the result that the repeatability of the time delay is upset.

Another disadvantage is that the repeatability of the timedelay setting depends on the counter-pressure in the line into which the working fluid is displaced from under the plunger of the relay. In most cases the same line accepts the working fluid returned from other elements of the hydraulic system, with the result that the pressure in the return line varies, and these variations affect the repeatability of the time-delay setting.

Still another disadvantage is that the time delay depends on the viscosity (temperature) of the working fluid, because the orifice has a finite length in the direction of flow, and viscous friction directly affects the accuracy of relay operation.

It is an object of the present invention to provide a hydraulic time relay for hydraulic systems, which ensures reliable and consistent repeatability of the time-delay setting through automatic cleaning of the orifice prior to each cycle of operation.

Another object of the present invention is to provide a hydraulic time relay for hydraulic systems, which ensures independence of the time-delay setting from variations in the counter-pressure in the return line of the hydraulic system.

Still another object of the present invention is to provide a hydraulic time relay for hydraulic systems, which has a time delay independent of variations in the working pressure and flow rate of the working fluid in the hydraulic system.

A further object of the present invention is to provide a hydraulic time relay for hydraulic systems, which can be charged (that is, whose barrel'can be filled with working fluid) under both the working pressure and the counter-pressure in the return line.

With these and other objects in view, in a hydraulic time relay for hydraulic systems, having a plunger periodically displacing a constant volume of fluid from the relay barrel through the orifice of a throttle plug, the throttle plug is, according to the invention, adapted to be reciprocated along its axis by a power element alternately acting on the ends of the throttle plug.

In order that the relay can be filled with working fluid under both the working pressure and any other pressure lower than the working one, it designates preferable to spring load one end of the throttle plug and to provide at least one duct in the other end, through which the hydraulic system communicates with the relay barrel for filling it at one of the extreme positions of the throttle plug.

In order that the time-delay setting can be made independent of the temperature (viscosity) of the working fluid, it is preferable to give the orifice of the throttle plug a conical shape, with the vertex of the cone pointing against the fluid flow being throttled.

The hydraulic time relay of the present invention provides for convenient and reliable .microm'etric time-delay adjustment and for the repeatability of time-delay settings irrespective of the cross-sectional area of the orifice, the viscosity (temperature) of the working fluid, and the working pressure and the counter-pressures in the return line.

Other objects and advantages of the invention will be better understood from the following description of preferred embodiments when read in connection with the following drawings, in which:

FIG. 1 is a rear view of a hydraulic time relay according to the invention;

FIG. 2 is a section along line I-I of FIG. 1;

F IG. 3 is a section along line II-II of FIG. 2;

FIG. 4 is a section along line III-III of FIG. 3;

FIG. 5 is a section along line lVIV of FIG. 3;

FIG. 6 is a section along line VV of FIG. 2;

FIG. 7 is a perspective view of the throttle plug of a hydraulic time relay according to the invention;

FIG. 8 shows a longitudinal section through a hydraulic time relay according to the invention, in the discharge position;

FIG. 9 shows a longitudinal section through a hydraulic relay according to the invention, in the time-delay position;

FIG. 10 shows a hydraulic relay according to the invention used in the hydraulic system of a metal-cutting machine whose tool is in an extreme position;

FIG. 11 shows a hydraulic time relay according to the invention, used in the hydraulic system of a metal-cutting machine, with the relay in the time-delay position;

FIG. 12 shows a hydraulic time relay according to the invention, used in the hydraulic system of a metal-cutting machine, with the tool in the reverse position;

FIG. 13 is a longitudinal sectional view of a hydraulic time relay according to another embodiment of the invention, with the relay in the charge position; and I FIG. 14 is a longitudinal sectional view of a hydraulic time relay according to the modification of the invention shown in FIG. 13 in the time-delay position.

Referring now to FIGS. 1 and 2, at 11 is the nearly prismatic body of the hydraulic time relay disclosed herein. At 12 and 13 are machined flats on the mutually perpendicular faces of the body (FIG. 2). Screws 14 (FIGS. 3,4 and 5) fasten a cover 15 of the relay to the flat 12. The flat 13 is used to mount the relay on a baseplate to be provided in the hydraulic system of a metal-cutting machine (not shown in the drawing). on the baseplate the body 11 is secured by screws (not shown in the drawing) screwing into tapped holes in the baseplate and passing freely through openings 16 (FIG. 1).

The body 11 has a chamber or barrel 17 (FIG. 2) with annular recesses 18, 19, 20 and 21. The barrel 17 is stoppered or closed by a plug 22 and a ring gasket 23. There is a longitudinal slot 24 in the barrel 17 between the recesses 20 and 21.

The barrel 17 contains a plunger 25 which is very closely fit in the body and has an undercut on its cylindrical surface, bounded by edges 26 and 27, and a leak-off undercut 28. The latter communicates with the space inside the plunger 25 through radial holes 29.

The bore of the plug 22 receives a finger 30 and a coil spring 31 which biases the plunger 25 against the cover 15 (when the relay is inoperative).

The body 11 also accommodates a check valve 32 with a spring 33 and a retainer 34. The joint between the body 11 and the cover 15 is sealed by a ring gasket 35. In the body 11 there is an annular recess 36 machined concentrically with the valve 32 and communicating with a pocket 37 through a radial hole 38 and an axial hole 39 in the valve 32.

On the side of the flat l3 (and at right angles to it) there is a duct 40 running through the annular recess 36 and into the recess 18, which lets in the flow of working fluid to be delayed. Running in parallel with the duct 40, there is another duct 41 to let out the delayed flow of working fluid, opening into the recess 19 and communicating with still another duct 42.

There are three more ducts made on the side of the flat 13 (likewise at right angles to it), namely an inlet duct 43 (FIGS. 1 and 4), an outlet duct 44 (FIGS. 1 and 5), and a leak-H duct 45 (FIGS. 1, 2 and 6). The latter opens into the longitudinal slot 24.

The inlet duct 43 and the outlet duct 44 communicate respectively with a duct 46 (FIG. 4) and a duct 47 (FIG. located in the body 11 on the side of the flat 12. At the joint between the body 11 and the cover 15, the ducts 46 and 47 are sealed by ring gaskets 48 and 49.

The ducts 40, 41, 43, 44 and 45 are sealed by ring gaskets 50,51, 52,53 and 54, respectively (FIG. 1).

The cover has a chamber 55 (FIG. 2) and annular recesses 56 and 57. On both sides of the chamber there are pockets 58 and 59. The pocket 58 receives a screw plug 60 threadedly held against a ring gasket 61. The pocket 59 receives a connection 62 also threadedly held against a ring gasket 61. The connection 62 is prevented from working loose spontaneously by a strap 63 secured by screws 64 (FIG. 3). The connection 62 (FIG. 2) has a threaded spindle 65 threadedly held against a washer 66. The spindle 65 is locked by a lock-nut 67.

The lock-nut 67 carries a zero-index cap 68, while the spindle 65 supports a thimble 69 with an arbitrary micrometric scale. The cap 68 and the thimble 69 are secured by screws 70. For each position of the graduated thimble relative to the zero index on the cap there is a certain definite position of a tip 71 of the spindle 65.

The chamber 55 accommodates a throttle plug 72 which is mounted into the chamber 55 with a close fit but free to reciprocate along its axis.

At the end facing the screw plug 60 the throttle plug 72 has a pintle 73 which is free to pass through the opening in a washer 74 held down by a spring 75. The other end of the spring 75 bears against the screw plug 60.

The throttle plug 72 has an orifice 76 (FIG. 7) conical in shape, with the vertex 77 of the cone pointing against the direction of fluid flow being throttled.

On the surface of the throttle plug 72 there is a circular inlet recess 78 communicating with the pocket 59 through a radial passage 79 and an axial passage 80 (FIG. 2) cut in the body of the throttle plug 72.

A duct 81 places the recess 56 in communication with an annular space 82 in the barrel 17. The recess 57 is placed in communication with the leak-off duct 44 by ducts 83 and 84 (FIG. 3) and the duct 47. The pocket 58 communicates with the pocket 37 and consequently with the duct 40 through ducts 85 and 86. The pocket 59 communicates with the duct 43 through ducts 87 and 88 (FIGS. 3 and 4) and the duct 46.

A cycle of the hydraulic time relay disclosed herein comprises two alternating positions: the charging of the relay, and the time delay.

The charging of the relay is such that the flow of working fluid is admitted into the inlet duct 43 from which it flows through the ducts 46, 88 and 87 into the pocket 59. On entering the power element acting on the end 89 (FIG. 2) of the throttle plug 72, the fluid causes the latter to move until its pintle 73 bears against the screw plug 60, thereby compressing the spring 75 through the washer 74 as shown in FIG. 8. When this happens, the inlet duct 78 is placed in communication with the recess 56, and the fluid leaves the pocket 59 to enter the pocket 82 through the ducts 80, 79 and 81. The plunger 25 overcomes the spring 31, moves back until it bears against the screw plug 22, and separates the recesses 18 and 19. In the meantime, the pocket 82 is filled with the maximum constant volume of working fluid. The flow of working fluid from the recess 56 into the recess 57 is shut off by the throttle plug '72. The time relay is charged.

The relay may be charged under either the pressure of the main flow (controlled by the relay) or any other lower pressure such as the control pressure in the system or the counterpressure in the return line of the hydraulic system. When using a pressure lower than that of the main flow for the charging purpose, this pressure may be left permanently applied to the relay, that is, not only during the charging interval, but also during the time delay. When using the pressure of the main flow for the charging purpose, this pressure should be alternately applied to the inlet duct 43 (for charging) and to the duct 40 (during the time delay).

The desired time delay is accomplished by feeding the main flow of working fluid into the duct 40. At first, the flow is shut off, since it cannot enter the duct 41 because the recess 18 is cut off by the plunger 25, and the check valve 32 is closed down by its spring 33 and the applied pressure.

At the same time, however, the pressure in the pocket 58 becomes equal to that of the applied main flow. This pressure causes the throttle plug 72 to move until its tip 89 comes in contact with the tip 71 of the threaded spindle 65 (the throttle plug is free to move in this direction since by the instant of the time delay the pressure in the pocket 59, as already noted, is either zero or lower than that of the main flow, depending on the pressure used to charge the relay). The throttle plug 72 occupies the position shown in FIG. 9. In this position, the recess 56 is shut off from the inlet duct 78 and is placed in communication with the recess 57 through the uncovered orifice 76. The spring 31 causes the plunger 25 to displace the fluid from the pocket 82 through the orifice 76, the recess 57 and the ducts 83, 84, 47 and 44 into a separate return line emptying directly into the reservoir (not shown in the drawing).

The time required to displace the fluid from the pocket 82 (that is, the time delay) depends on how much of the orifice 76 is uncovered, which is in turn determined by the position of the threaded spindle 65.

After all fluid has been displaced from the pocket 82, the plunger 25 again bears up against the cover 15, and the undercut on the cylindrical surface of the plunger 25 bounded by the edges 26 and 27 places the recess 18 in communication with the recess 19, and the working fluid is free to flow from the duct 40 to the duct 41. The time delay is over.

As follows from the above description of an operating cycle of the hydraulic time relay disclosed herein, within each cycle the throttle plug 72 alternately covers and uncovers the orifice 76 as the relay changes over from charging to the time delay. Because of this, the orifice is cleaned each time, and its clogging (usually occurring with the orifices in stationary throttles) is prevented, so that the out-flow of working fluid from the pocket 82 takes place under stable conditions and there is a consistent repeatability in the time-delay setting.

When the relay is being charged with the main flow, it usually takes some time for the flow to be switched over from charging to the time delay (either because the respective distributor in the hydraulic system cannot be switched over instantaneously, or for some other causes). In such a case (after the pressure has been removed from the pocket 59) the throttle plug 72 is forced by the spring 75 and the washer 74 to move in the direction of the threaded spindle 65. However, since there is no pressure applied to the pocket 6 58 yet, the throttle plug 72 moves only until the washer 74 touches the bottom of the pocket 58. In this position the recess 56 is shut off by the throttle plug 72, and the fluid cannot flow out of the pocket 82 (this position of the throttle plug is shown in FIGS. 2 and 3). Further movement of the throttle plug 72 until it touches the tip 71 of the threaded spindle 65 becomes possible only after pressure is applied to the pocket 58, after which the time delay is effected in the manner already described. In this way the time delay is made independent of the time required to switch over the main flow from charging to the time delay.

Since the fluid is caused to flow out of the pocket 82 by the spring 31 into a separate return line communicating with the duct 44, the value and repeatability of the time delay are not affected by variations in the hydraulic systems working pressure, counter-pressure in the common return line, and the flow rate of working fluid.

Since the effective cross-sectional area of the orifice 76 in the throttle plug 72 is controlled by the sharp edge of the recess 56, variations in the viscosity of the working fluid in the hydraulic system with temperature have no effect on the repeatability of the selected time-delay setting.

As is seen, the embodiment of the hydraulic time relay just described accomplishes all the objects of the present invention.

The purpose of the check valve plug 32 is to return the reverse flow into the return line from the duct 41 to the duct without a time delay, irrespective of the position of the plunger 25. The leak-off duct serves to return fluid leakage into the line. The purpose of the recess 20 and the slot 24 is to prevent false operation of the plunger 25 (especially in the case of long time delays) by returning the fluid which happens to leak along the plunger 25 (clearance leakage) into the duct 45.

As an illustration of operation of the hydraulic time relay in conjunction with other elements of a hydraulic system, FIGS. 10 and 11 -..and 12 show one of the possible schemes in which a hydraulic time relay provides for a controlled time delay of the tool of a metal-cutting machine in one of the extreme positrons.

The main pressure line delivers working fluid through a distributor (positioned as shown in FIG. 10) into a power cylinder 91, so that the tool of the machine moves to the right in the direction of the arrow A. At the same time, a pilot valve 92 is so positioned that the fluid coming from a control pressure line 93 is distributed by a line 94 both into a pocket in the distributor 90, and in the pocket 59 through the inlet duct 43 and the ducts 46, 88 and 87. The pressure of the fluid in the pocket 59 causes the throttle plug 72 to move to the right,

thereby overcoming the spring 75. As this happens, the fluid flows from the pocket 59 through the ducts 80, 79 and 78 into the recess 56 from which it flows through the duct 81 into the pocket 82. At the same time, the plunger 25 overcomes the spring 31 and moves to the lowermost position. The relay is charged.

As the tool of the machine approaches a limit stop 96, a cam 97 mounted on the moving part of the tool switches a pilot valve 92 into the other extreme position (FIG. 11) in which the fluid coming from the control pressure line 93 is conveyed by a line 98 to the duct 40.

At the same time, the line 94 is placed in communication with a return line 99. The pressure of the fluid fed to the duct 40 causes the throttle plug 72 to move to the right until it touches the tip 71 of the threaded spindle 65. This uncovers the orifice 76 to the extent predetermined by the setting of the spindle 65, so that the fluid will flow from the pocket 82 into a separate return line 100 at a certain definite rate.

As already noted, from the pocket 82 the fluid is displaced under the action of the spring 31. It cannot flowfrom the pocket 82 into the pocket 59, since the passage is shut off by the throttle plug 72.

The time delay continues until the predetermined volume of fluid has fully flown from the pocket 82. After that, the plunger 25 places the recesses 18 and 19 in communication, as shown in FIG. 12, and fluid flow is directed from the duct 40 to the duct 41 and further down a line 101 into a pocket 102 of the distributor 90 whose spool, on moving to the left places the main pressure line in communication with the power cylinder 91. After the predetermined period of time governed by the time-delay setting of the relay the tool is moved in the reverse direction along the arrow B. In the leftmost position a cam 103 of the tool switches over the pilot 92 to the original position, and the cycle is repeated again. The check valve 32 provides for the flow of fluid without a time delay from the pocket 102 into the return line as the fluid is fed into the pocket 95.

The above-described construction and connection of the hydraulic time relay disclosed herein are only an example of a preferred embodiment and application of the operating principle set forth and do not limit modifications and adaptations which may be made.

FIGS. 13 and 14 show a second embodiment of the relay disclosed herein, constructed on the same principle. This embodiment comprises mainly the same elements as the previous one, but somewhat differs from the latter in layout, method of connection, and some of its capabilities.

A body 104 has a chamber or barrel 105 with annular recesses 106 and 107, and an operating space 108. The barrel 105 is closed by a cover 109 over a paper gasket.

The barrel 105 holds a plunger 110 which is mounted to closely fit in the barrel and has an undercut on its cylindrical surface, bounded by edges 111 and 112. The bore of a plunger 110 houses a spring 113 which biases the plunger against the end of the barrel 105 on the side of the space 108 when the relay is inoperative.

The body 104 also holds a check ball valve 114 with a spring 115 and a retainer 116. A space 117 is placed in communication with an inlet duct by a drilling 118 and a duct 119 passing through the recess 106, while a duct 121 communicates with an outlet duct 122 which is in turn in communication with the recess 107.

The body 104 also holds an inlet check valve 123 with a spring 124 and a retainer 125. A space 126 communicates with the space 108 through a hole 127, and a duct 128 communicates with an inlet duct 129.

Placed in parallel with the barrel 105 but on the opposite side of the body 104 there is a barrel 130 with annular recesses 131, 132 and 133. The recess 131 communicates with the ducts 128 and 129, the recess 132 communicates with the space 108 in the barrel 105 through a hole 134, and the recess 133 communicates with a return duct 135. The barrel 130 accommodates a sleeve 136 held up to the end of the chamber by a cover 137 through a washer 138. On its external surface the sleeve 136 has annular grooves which are in register with the recess 132 and 133, while the lands on the sleeve carry ring gaskets 139. The sleeve 136 has two recess 140 and 141 which communicate with the recesses 132 and 133, respectively, through radial holes, and also a conical slot between the recesses 140 and 141, with the vertex of the cone pointing against the fluid flow being throttled. The bore 130 of the sleeve 136 holds a throttle plug 142 which is mounted to closely fit in the bore but is free to reciprocate along its axis, with a conical orifice 143 on its surface, the vertex of the cone pointing against the direction of fluid flow being throttled. This orifice in conjunction with the said slot in the sleeve 136 determine the cross-sectional area of the passage for the working fluid.

When the end of the throttle bears up against the washer 138, the orifice 143 is fully covered by the recess 141, so that the recesses 140 and 141 are separated by the throttle plug 142. When the opposite end of the throttle plug 142 bears up against the tip 71 of the spindle 65 (built into a cover 137 identical in construction with that already described), the passage between the recesses 140 and 141 is uncovered for the flow of working fluid to the extent dependent on the setting of the spindle 65.

The space 144 facing the tip 71 of the spindle 65 communicates through a hole 145 in the cover 137 with the recess 131 and, consequently, with the inlet duct 129. The opposite space 146 communicates through a hole 147 in the relay body 104 and through a hole 148 in the washer 138 with the duct 119 and, consequently, with the inlet duct 120.

The cover 109 has a leak-off duct 149 which serves to return fluid leaks into the system.

As is the case with the first embodiment of the hydraulic time relay disclosed herein, the second embodiment has an operating cycle consisting of two alternating positions: charging of the relay and the time delay.

The relay is charged by feeding a flow of working fluid through the inlet duct 129, the duct 128, the inlet check valve 123 and the hole 127 into the space 108. The pressure of the fluid entering the power element, acting on the end of the throttle plug 142 from the side of the space 144, causes the throttle plug 142 to move until it touches the washer 138, thereby shutting off the outflow of fluid from the space 108 through the hole 134, the recesses 132, 140, 141 and 133 into the return duct 135.

The pressure in the space 108 causes the plunger 110 to overcome the spring 113 and to move back until it bears up against the cover 109, thereby separating the recesses 106 and 107. At this instant, the space 108 is filled with maximum constant volume of fluid. The relay is charged.

The time delay is effected by feeding the main flow of fluid to the inlet duct 120. At first, the applied flow is shut ofi, since it cannot reach the duct 122 as the recesses 106 and 107 are isolated from each other by the plunger 110 while the check valve 114 is closed by its spring 115 and the applied pressure. However, the pressure in the space 146 becomes equal to the applied pressure. This pressure, acting on the end of the throttle plug 142, causes the latter to move until its opposite end touches the tip 71 of the threaded spindle 65.

The throttle plug 142 can move in the indicated direction because at the instant when the time delay is to be effected there is no pressure in the space 144.

It is relevant to note that this embodiment of theinvention substantially differs from the previous one in a very important respect. This difference consists in that the charging pressure, even lowered in comparison with the pressure of the main flow applied to the duct 120, cannot be applied to the inlet duct during the time delay, since otherwise the fluid would force its way through the check valve 123,-the space 108 and the orifice 143 into the return duct 135, so that there would be a continuous inflow of fluid into the space 108, and no time delay would be effected.

The throttle plug 142 takes up the position shown in FIG. 14. At the same time, it uncovers the orifice 143 to the extent dependent on the setting of the tip 71 of the spindle 65, so that the recess 140 is placed in communication with the recess 141. Under the action of the spring 113, the plunger 110 displaces the fluid from the space 108 through the hole 134, the recesses 132 and 140, the orifice 143, the recesses 141 and 133 into the return duct 135 connected by a pipeline directly with the reservoir (not shown in the drawing). No fluid can be displaced through the opening 127, since the check valve 123 closes.

The time required for the fluid to be completely displaced from the space 108 depends on the extent to which the orifice 143 in the throttle plug 142 is uncovered, which is in turn determined by the setting ofthe spindle 65.

After all fluid has been displaced from the space 108, the plunger 110 again comes to bear upon the end of the barrel 105, and the undercut on the cylindrical surface of the plunger, bounded by the edges 111 and 112, places the recess 106 in communication with the recess 107, and the applied stream of fluid is free to flow from the duct 120 to the duct 122. The time delay is over.

As in the previous embodiment (FIGS. 1 through 12), the

throttle plug 142 alternately covers and uncovers the orifice 143 as the relay is switched over from charging to the time delay. Because of this, the orifice is automatically cleaned, thereby providing for the consistent repeatability of the time delay.

As in the previous embodiment, the fluid from the space 108 is returned into a separate line, which fact eliminates any effect of variations in the hydraulic systems operating pressure, counter-pressure in the common return line of the hydraulic system and the flow rate of working fluid on the magnitude and repeatability of the time-delay setting.

As in the previous embodiment, the conical orifice 143 makes the time-delay setting practically independent of variations in the viscosity of the working fluid with temperature in the hydraulic system.

This latter embodiment differs from the previous one in that during the time delay the counter-pressure in the line communicating with the inlet duct 129 cannot be higher than the pressure produced by the spring 113 of the plunger 110 in the space 108, since otherwise, as already noted, the space 108 would be continuously re-filled through the check valve 123,

and the time-delay setting would be disturbed.

In other respects the embodiment shown in F lGS. 13 and 14 does not differ in the principle of operation or construction from the embodiment shown in FIGS. 1 through 12. lts functioning in, for example, the system shown in FIGS. 10, 11 and 12 does not differ from that of the previous embodiment in the same system.

The check valve 114 serves the same purpose as the valve 32, namely: to allow the fluid to flow from the duct 122 to the duct and into the return line without a time delay, irrespective of the position of the plunger 110.

As is seen, the operating principle of the hydraulic time relay, described in the foregoing, may be utilized in a variety of structural modifications and functional schemes, including those not mentioned here.

The hydraulic time relay disclosed herein provides for the repeatability of the time-delay setting accurate to within $0.5 percent at a steady-state temperature in the hydraulic system and within fl or 3 percent with the temperature in the hydraulic system rising or falling by 20 to 30 C.

What is claimed is:

1. A hydraulic time relay for hydraulic systems, comprising a body with a charging duct and, at least, one inlet duct and one outlet duct respectively for supplying and discharging the fluid flow being checked; said body having a first barrel with an end portion in communication with said charging duct, a check valve controlling communication between said first barrel and said charging duct, a movable plunger in said first barrel having a passage therein and, with the plunger in one extreme position thereof providing intercommunication between the inlet and outlet ducts to permit fluid flow therethrough; said body having a second barrel with undercuts in a central portion thereof by which the second barrel is in communication with said end portion of said first barrel and with the discharge duct; said second barrel having end portions one of which is in communication with said charging duct, and the opposite end of which is in communication with said inlet duct; said second barrel having an adjustable stop and including a movable slide valve therein which can reciprocate under the action of pressure drops in the end portions of said second barrel; said slide valve including means which in combination with said second barrel define a throttling orifice for the passage of the fluid forced out of the first barrel by said plunger into the discharge duct when the slide valve is in an extreme position as determined by said adjustable stop.

2. A hydraulic time relay for hydraulic systems, comprising a body with a charging duct and, at least, one inlet orifice and one outlet orifice respectively for supplying and discharging fluid flow being checked; said body having a first and a second barrel communicating with each other; a plunger in said first barrel and having a passage therein which intercommunicates the inlet and outlet orifices to periodically let the fluid flow therebetween when the plunger is in one of two extreme positions thereof; said second barrel having two opposite end portions one of which is in communication with the charging duct and the other of which is connected with said outlet orifice; said second barrel having an adjustable stop, and a movable slide valve in said second barrel having an end portion disposed at the side of the inlet duct which is spring loaded and an opposite end portion provided with at least one duct communicated with that end portion of the second barrel connected with the charging duct to provide communication between the latter and said first barrel and to fill the first barrel when the slide valve is in one of two extreme positions thereof; said slide valve including means which in combination with the second barrel defines a throttling orifice for the passage of the fluid forced out of the first barrel by said plunger into the discharge line when the slide valve is in the extreme position thereof determined by said adjustable stop. 

1. A hydraulic time relay for hydraulic systems, comprising a body with a charging duct and, at least, one inlet duct and one outlet duct respectively for supplying and discharging the fluid flow being checked; said body having a first barrel with an end portion in communication with said charging duct, a check valve controlling communication between said first barrel and said charging duct, a movable plunger in said first barrel having a passage therein and, with the plunger in one extreme position thereof providing intercommunication between the inlet and outlet ducts To permit fluid flow therethrough; said body having a second barrel with undercuts in a central portion thereof by which the second barrel is in communication with said end portion of said first barrel and with the discharge duct; said second barrel having end portions one of which is in communication with said charging duct, and the opposite end of which is in communication with said inlet duct; said second barrel having an adjustable stop and including a movable slide valve therein which can reciprocate under the action of pressure drops in the end portions of said second barrel; said slide valve including means which in combination with said second barrel define a throttling orifice for the passage of the fluid forced out of the first barrel by said plunger into the discharge duct when the slide valve is in an extreme position as determined by said adjustable stop.
 2. A hydraulic time relay for hydraulic systems, comprising a body with a charging duct and, at least, one inlet orifice and one outlet orifice respectively for supplying and discharging fluid flow being checked; said body having a first and a second barrel communicating with each other; a plunger in said first barrel and having a passage therein which intercommunicates the inlet and outlet orifices to periodically let the fluid flow therebetween when the plunger is in one of two extreme positions thereof; said second barrel having two opposite end portions one of which is in communication with the charging duct and the other of which is connected with said outlet orifice; said second barrel having an adjustable stop, and a movable slide valve in said second barrel having an end portion disposed at the side of the inlet duct which is spring loaded and an opposite end portion provided with at least one duct communicated with that end portion of the second barrel connected with the charging duct to provide communication between the latter and said first barrel and to fill the first barrel when the slide valve is in one of two extreme positions thereof; said slide valve including means which in combination with the second barrel defines a throttling orifice for the passage of the fluid forced out of the first barrel by said plunger into the discharge line when the slide valve is in the extreme position thereof determined by said adjustable stop. 